Device and method for a layerwise manufacturing of a three-dimensional object from a building material in powder form

ABSTRACT

A method is provided, by which a three-dimensional object is manufactured by a subsequent solidification of layers of a building material in powder form at the positions in the respective layer that corresponds to the cross-section of the object by means of the action of a laser or another energy source, 
     wherein as building material in powder form a material is used which contains the old powder that has remained as unsolidified powder in the manufacturing of one or more previously formed objects and a proportion of new powder that has not been used before in any manufacturing process,
 
characterized in that
 
the building material in powder form is mechanically consolidated when a layer is applied.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 11/994,285, filed on May 27, 2008, which is a national stageentry of PCT/EP2007/003641, filed Apr. 25, 2007, and claims priority toDE 102006023484.7, filed May 18, 2006, the entire contents of each ofwhich are incorporated herein by reference.

The invention is related to a device and a method for a layer-wisemanufacturing of a three-dimensional object from a building material inpowder form. In particular, the invention is related to a method forselective laser sintering, in the following briefly called lasersintering method, and to a laser sintering device.

A laser sintering method and a laser sintering device according to thepreamble of claims 1 and 5, respectively, are, for example, known fromDE 101 05 404 A1. In the method particularly a plastic powder such aspolyamide is used.

In the known method for each building process a specified amount of oldpowder, i.e. powder, which remains from one or several previous buildingprocesses, is used. However, the old powder is subject to an agingprocess.

For example the old powder is thermally and/or thermooxidatively damagedand thus has other material properties and for this reason also otherprocessing parameters than new powder. Therefore, it can be added to thenew powder only in defined proportions in order not to put at risk thebuilding process and the part quality. The so-called refresh rate is thevalue of the percentage of new powder in the mixed amount/percentage ofold powder in the mixed amount (e.g. 50/50) that is used for a buildingprocess. This refresh rate shall be as small as possible, because thenthe costs for new powder can be saved.

In DE 101 05 504 A1 it is proposed to preprocess the old powder or amixture of old powder and new powder before the solidification, forexample by fluidizing, in order to reduce the effect of aging-relatedquality-reducing changes such that more old powder can be added.

By such a pre-treatment, however, usually not all aging-relatedquality-reducing changes of the powder can be eliminated. In particular,a too high proportion of old powder gives rise to an unsatisfactorysurface quality of the outer walls of the part due to dip positions,which are also called “sink marks” or “orange peel”.

From WO 2005/097475 a laser sintering method and a laser sinteringpowder for such a method are known, wherein it is attempted to solve theproblem of the dip positions by using a certain material that has anincreased stability in the laser sintering process and thus has feweraging-related damages, when it is used as old powder. However, in thatcase the user is dependent on the use of this specific powder which inturn has different properties than the familiar powder used up to thattime and possibly does not meet all demands.

Furthermore, from U.S. Pat. No. 4,938,816 it is known to compact thepowder in laser sintering by generating an electromagnetic field duringor before the solidification with the laser.

From EP 1 058 675 B1 it is known to compact an applied powder layer bymeans of a roller in the layer sintering of a ceramics powder. Therebythe time shall be reduced, which is required in the sintering in thesolid phase of the ceramics powder.

From DE 195 14 740 C1 a device for laser sintering, in particular ofmetal powder, is known, in which the powder is applied by means of anapplication blade. The blade has at the application edge a beveled edgehaving an angle between 30° and 90°. A beveled face, which has an anglebetween 1° and 60° is also provided at the opposing smoothing edge. Thesmoothing edge smoothes an already solidified layer.

It is an object of the invention to provide a method and a device forproducing a three-dimensional object, in particular a laser sinteringmethod and a laser sintering device, by which the refresh rate can bereduced and by which the costs of the process can be reduced.

The object is achieved by a device according to claim 1 and a methodaccording to claim 7, 8 or 13. Further developments of the invention aredescribed in the dependent claims.

The method has the advantage that conventional powder for lasersintering such as polyamide or other families, in particularpolyaryletheretherketone (PEEK), in each case with and without additionssuch as glass particles, reinforcing fibers, metallic additions as e.g.aluminum-filled polyamide and others, can be used, the properties ofwhich are sufficiently known. Furthermore, by the method and the devicethe refresh rate can be reduced up to 0% new powder (0/100).

Further features and utilities of the invention arise from thedescription of embodiments based on the figures, of which:

FIG. 1 shows a schematic representation of a laser sintering device; and

FIG. 2 shows a schematic perspective side view of the powder applicationby means of an application device in the laser sintering device;

FIG. 3 shows a schematic representation of the cross-section of theapplication blade of the application device; and

FIG. 4 shows a schematic partial cross-sectional perspective view of howthe application device applies powder onto an already sintered layer.

The laser sintering device shown in FIG. 1 comprises a container 1,which is open to the top and has therein a support 2 that can be movedin a vertical direction, supports the object 3 to be formed and definesa building field. The support 2 is adjusted in the vertical directionsuch that the respective layer of the object, which layer is to besolidified, lies in a work plane 4. Further, an application device 5 forapplying the building material in powder form, which is to be solidifiedby means of electromagnetic radiation, is provided. The device comprisesalso a laser 6. The laser beam 7 that has been generated by the laser 6is directed onto a coupling window 9 by means of a deflection device 8,which lets the laser beam 7 pass into the process chamber 10 and focusesit to a predetermined point in the work plane 4.

Furthermore, a control unit 11 is provided through which the componentsof the device are controlled in a coordinated manner in order to performthe building process.

As is shown in FIG. 2, the application device comprises two jaws 51, 52that are arranged at a distance to each other and at a distance abovethe work plane, wherein the powder supply 20 is located between thesetwo jaws 51, 52. The jaws 51, 52 extend across the whole width of thebuilding field. On the inner sides of the jaws, which are facing eachother, blades 60, 61 are provided, which also extend across the wholewidth of the building field and which protrude at the jaw downwardstowards the work plane. The bottom side of the blade has a distance dfrom the support surface or the layer that was solidified last, whereinthe distance d corresponds to the layer thickness of the desired layer.In FIG. 2 the present direction of movement of the application device 5,which is shown, is indicated by B.

As can be seen in FIG. 3, the blade has a thickness D in the directionof movement B and has two surfaces 60 a, 60 b that are extendingsubstantially perpendicular to the work plane 4 and are alignedsubstantially in parallel to each other, which extend transverselyacross the building field. At its bottom side facing the work plane theblade has a sloping surface 60 c, wherein the blade is positioned in theapplication device such that the sloping surface 60 c ascends in thedirection of application B. The sloping surface forms an applicationsurface. Together with a surface E that is in parallel to the work plane4 and the support surface, respectively, it includes an acute angle α,which lies between a value larger than 0° and approximately 5°,preferably at approximately 2°. The lower edge 60 d between theperpendicular surface 60 b and the sloping blade surface 60 c is at aheight x with respect to the plane E. When the blade has a thickness Dof approximately 6 mm, the height x is larger than 0.03 and smaller thanapproximately 0.5 mm. The thickness of the blade can be between 1 mm and20 mm. Thereby the application device has only a small angle ofincidence of the surface 60 c in the application direction B.

The second application blade 61 is arranged at the inner side of thesecond jaw 52 and is formed such that it is mirror-symmetrical to thefirst application blade 60. Thus, the beveled surface 61 c of the secondapplication blade 61 has an angle of incidence opposite to theapplication direction B, in which the first application blade 60performs the application operation. Thereby it is possible to apply anew powder layer by means of the application device during the forwardmovement and the backward movement, respectively, and to respectivelytake along the powder supply and if necessary supplement it.

In operation preferably a plastic powder, for example a polymer powdersuch as polyamide, in particular polyamide 12, or a powder from anotherfamily such as PEEK, in each case with or without additions, is used aspowder. Before the application operation old powder, which remains asnot sintered powder from one or several previous building processes, ismixed with new powder. For example, for unfilled polyamide the refreshrate is 50%-30% of new powder (refresh rate 50/50 to 30/70) and forfilled polyamide the refresh rate is 100%-70% of new powder (refreshrate (100/0 to 70/30). The term “new powder” describes a powder that hasnot been used in any previous manufacturing step. The term “old powder”describes a powder consisting of approximately 90% powder, which isco-inserted into the powder cake and is stored under a high temperaturefor the whole duration of the building process, and approximately 10%powder, which has been shifted into overflow containers during the layerapplication.

The mixing can take place outside or inside the laser sintering device.Before each application operation the powder is added in the applicationdevice 5 in an amount that is sufficient for applying a layer of thepowder.

Then the application device 5 moves across the building field, whereinthe application blade 60 applies a layer 21 having the predeterminedthickness d. As the surface 60 c is sloped with respect to the directionof application B, a force acts onto the powder to be spread, whichpowder is positioned in the powder column located in front of theapplication blade 60, wherein the force is directed into the work plane.Thereby the powder 20 is compressed during the application of the layer.

Then the cross-section of the object 3 in the respective laser isirradiated with the laser beam and thus the powder is solidified.Afterwards the application device 5 is again filled with powder and ismoved in a direction opposite to the direction B shown in FIGS. 2 and 3.Thereby the second application blade 62, which is formedmirror-symmetrically to the first application blade 60, acts asapplication device and applies a new powder layer onto the lastsolidified layer and the powder surrounding the solidified region,respectively.

FIG. 4 explains schematically the operation of the blade according tothe invention. The object 3 comprises a plurality of already solidifiedlayers 21 and not sintered powder 22 surrounding these layers. The lastapplied and solidified layer comprises an already solidified portion 23a and not sintered powder 23 b. As the density increases during thesolidification, the already solidified region 23 a is slightly loweredwith respect to the level of the unsolidified powder 23 b. Thereby edges24 are formed between the already solidified portion 23 a and theunsolidified region 23 b.

When the blade 60 according to the invention is used, it was observedwith surprise that a compression pressure acts on the particles in thelayer and there are marginal or no dip positions in the completed part.

By increasing the powder bed density it is not only possible to reducethe refresh rate, but also to use a powder, which up to now is not oronly to a limited extent suited for the laser sintering process.

The powder bed density is measured as follows: A closed hollowthin-walled block-shaped laser sintering part is exposed such that theenclosed volume during the exposure has a value 100 mm×10 mm×15 mm inthe directions xyz. The volume surrounding the part has to bedimensioned correspondingly. Adhering powder remnants are removed fromthe outside of the thus manufactured part and the thus manufactured partis weighed. Thereafter the part is cut open and the powder inside isdrained and the empty part is again weighed. The difference between themasses corresponds to the mass of the enclosed powder volume. As thepowder volume is known, the density of the powder bed can be calculatedfrom it.

The following table shows a result of the device according to theinvention and of the method compared to the prior art. Polyamide 12,which can be obtained under the trade name PA 2200 (sintering powder ofthe applicant for the EOSINT P machine) was used as laser sinteringpowder. The applied layer thickness was 0.15 mm:

Aging Blade geometry condition Solution [width (mm)/ of the powderviscosity Minimum compressed % new according powder bed density (mm)powder/% to ISO density Results for old powder 307 [η rel] [g/cm³]single bevel 50/50 2.1 0.4 6/0.08 25/75 2.35 0.41 6/0.15  0/100 2.6 0.436/0.3 

The solution viscosity of the powder was determined according to ISO307, the powder bed density was determined according to theabove-described method.

By the method and the device, respectively, the required proportion ofnew powder can be reduced. In an exceptional case it is even possible towork with nearly 100% of old powder. Furthermore, the table shows thatthe solution viscosity, which is a measure for the melt viscosity of thematerial, increases with the proportion of old powder. Therefore, by themethod according to the invention it is also possible to sinter alsopowder materials that have a correspondingly high melt viscosity andcould not be processed by the methods and devices existing hitherto.Polyamide (PA), in particular PA 12, is advantageously suited for thedevice and the method, because it can be manufactured by a precipitationprocess and therefore has a particularly smooth surface compared to amilled powder. Therefore, settling processes can advantageously takeplace during the application.

The geometry of the application device is not limited to thespecifically shown embodiment. For instance, the surfaces 60 a, 60 bneed not be in parallel and shaped surfaces are also not excluded.

The ascending slope of the application surface need not be constant, butmay also ascend in a different way, e.g. may be scaled or may have adifferent shape.

Instead of a laser also a different energy source, which is suited forthe solidification of a material in power form such as an electron beamsource can be used. Also other ways of an energy entry are possible suchas mask sintering, inhibition sintering or a line-shaped energy entry oran energy entry via an array.

The invention claimed is:
 1. Method for manufacturing athree-dimensional object by a subsequent solidification of layers of abuilding material in powder form at those positions in the respectivelayer that correspond to the cross-section of the object by the actionof a laser or a different energy source, wherein a powder is used thathas a solution viscosity according to ISO 307 which is larger than 2.1ηrel and wherein the powder is mechanically consolidated during theapplication of a layer by using an application device comprising a bladewith an application surface, that rises in the direction of theapplication, wherein the application surface is provided at the bottomside of the blade and rises under an angle which lies in the rangebetween 1.43° and 2.86° in the direction of movement of the applicationdevice.
 2. Method according to claim 1, characterized in that a powderbed density is produced which is larger than 0.4 g/cm³.
 3. Methodaccording to claim 1, characterized in that as building material inpowder form a material is used, which comprises old powder that hasremained as unsolidified powder in the manufacturing of one or severalpreviously formed objects and new powder that has not been used beforein any manufacturing process.
 4. Method according to claim 1, wherein asbuilding material in powder form a material is used, which contains theold powder that has remained as unsolidified powder in the manufacturingof one or several previously formed objects and a proportion of newpowder that has not been used before in any manufacturing step,characterized in that the building material in powder form ismechanically consolidated when applying a layer and the proportion ofnew powder is smaller than 50% of the total amount of powder used forthe building process.
 5. Method according to claim 1, characterized inthat the object manufactured by the method does not have any dippositions.
 6. Method according to claim 3, characterized in that theobject manufactured by the method does not have any dip positions. 7.Method according to claim 2, characterized in that a powder bed densityis produced which is larger than 0.41 g/cm³.
 8. Method according toclaim 7, characterized in that a powder bed density is produced which islarger than 0.42 g/cm³.
 9. Method for manufacturing a three-dimensionalobject by a subsequent solidification of layers of a building materialin powder form at those positions in the respective layer thatcorrespond to the cross-section of the object by the action of a laseror a different energy source, wherein a powder is used that has asolution viscosity according to ISO 307 which is larger than 2.3η reland wherein the powder is mechanically consolidated during theapplication of a layer, characterized in that a powder bed density isproduced which is larger than 0.4 g/cm³.
 10. Method according to claim9, characterized in that the solution viscosity according to ISO 307 islarger than 2.6η rel.
 11. Method according to claim 1, wherein thematerial contains PA
 12. 12. Method for manufacturing athree-dimensional object by a subsequent solidification of layers of abuilding material in powder form at those positions in the respectivelayer that correspond to the cross-section of the object by the actionof a laser or a different energy source, wherein a powder is used thathas a solution viscosity according to ISO 307 which is larger than 2.3ηrel and wherein the powder is mechanically consolidated during theapplication of a layer.
 13. Method according to claim 12, characterizedin that the solution viscosity according to ISO 307 is larger than 2.6ηrel.
 14. Method according to claim 9, characterized in that a powder beddensity is produced which is larger than 0.41 g/cm³.
 15. Methodaccording to claim 10, characterized in that a powder bed density isproduced which is larger than 0.41 g/cm³.
 16. Method according to claim15, characterized in that a powder bed density is produced which islarger than 0.42 g/cm³.
 17. Method according to claim 14, characterizedin that a powder bed density is produced which is larger than 0.42g/cm³.